Clinical and ethical issues concerning medical decision-making capacity (MDC) frequently arise following traumatic brain injury (TBI). Patients with TBI often abruptly experience impairment or loss of MDC at time of injury, and then slowly regain decisional abilities during rehabilitation and recovery. Yet from time of acute injury, and throughout the rehabilitation and recovery period, patients and/or family members must make ongoing and often complex medical treatment decisions. Thus, following TBI, clinicians and hospitals must immediately address whether a patient has MDC and, in cases where MDC has initially been lost, continue to assess over time whether the patient has regained MDC. These circumstances of abrupt initial impairment and subsequent gradual recovery of MDC are unique to TBI and conditions like stroke, and present important clinical and ethical challenges. Yet surprisingly little is currently known empirically about MDC in patients with TBI. The natural history of impairment and recovery of MDC in TBI remains unknown. Clinicians, hospitals, and rehabilitation centers currently need empirical knowledge about MDC to inform and support decisions to permit, restrict or restore TBI patients'decisional autonomy. In addition, little is known about neurocognitive changes in TBI that presumably mediate changes in decisional capacity. Neurocognitive models can clarify the relationship of evolving decisional capacities to measures of cognitive outcome, and identify cognitive markers of decisional capacity in TBI. In this R01 project, we propose to study MDC empirically and longitudinally (baseline, 6 month, 12 month assessments) over a one-year period in a sample of 80 controls and 150 patients with TBI using objective capacity and neuropsychological measures, and also clinician judgments. TBI patients will be stratified (50 mild, 50 moderate, 50 severe) to understand how injury severity affects impairment and recovery of MDC over time. Aim 1 will investigate initial levels of impairment, rates of improvement, and extent of recovery of consent abilities in TBI patients (stratified by injury severity) over the one year period of spontaneous recovery characteristic of TBI. Aim 2 will test cross- sectional and longitudinal cognitive models of MDC in TBI patients, and identify cognitive markers of MDC in TBI.